1. Field of the Invention
The invention is related to micro-electro-mechanical systems (MEMS) and methods of making these systems.
2. Description of the Prior Art
In neurobiology, to study the central nervous system, electro physiologists use electrodes (referred to herein as recording electrodes) placed in the extra-cellular medium to record the activity of multiples neurons simultaneously. The variation of the local electrical potential is detected or recorded due to the action potentials (spikes) occurring in the surrounding neurons. By using more than one electrode, it is then possible to distinguish action potentials coming from different neurons due to the variation of the shape of the spike while traveling in the extracellular media. This way, each neuron firing will have a distinctive signature of spikes on the multiples electrodes as illustrated in FIG. 1.
The problem of associating a specific spike's signature on the electrodes to a specific neuron is called spike sorting. While simple tetrodes made of wires twisted together have been and are still in use, micro-machined electrode arrays are now becoming more and more common. Their main advantages are the consistency from one probe to the other compared to manually fabricated probes and the control over the dimensions and spacing of multi electrodes.
The micromachined neural probes have limited spatial resolution. The distance between recording pads are larger than 20 microns, which is generally larger than the size of neurons. The present inventors realized that these probes cannot be effectively utilized to probe neighboring neurons. Furthermore, the present inventors realized that these probes are more expensive than desired because they are made using expensive silicon processing steps, such as reactive ion etching (RIE) and plasma-enhanced chemical vapor deposition (PECVD).